This invention relates to an apparatus for securing a valve to the inside of a wrapper sleeve in a production line operation. The wrapper sleeve has at least one thermoplastic layer, and the apparatus includes a welding device as well as a mechanism for guiding the individual valves to the welding device.
Certain wrapped contents generate gases which, in case the wrapper is airtight, cause an excessive pressure that may result in an undesired inflation of the package. It has been known to provide gastight bags with a relief valve (excessive pressure valve) through which the gas may escape from the bag. Such valves are disclosed, for example, in German Auslegeschrift (Application Published after Examination) No. 1,903,048 or German Offenlegungsschrift (Application Published without Examination) No. 2,848,834.
While the valve, according to the Auslegeschrift, is secured to the inside of the bag wall and projects through a circular opening in the wall only with a valve head portion, the valve disclosed in the Offenlegungsschrift is secured to the outside of the bag. In this last-named structure, as indicated by the Offenlegungsschrift, spacers are necessary to prevent damaging of the valve or an unintended opening thereof. It is a disadvantage of externally arranged valves that the risks of an accidental tearing-off of the valves are high; this would result in a hole in the package. This reason alone warrants the positioning of the valve inside the bag. The valve may be provided with devices which prevent particles of the packed goods from penetrating into the valve. If a circular opening in the bag can be dispensed with (for example, if a slot suffices), the movable flap above the valve aids in preventing dirt or other material from penetrating into the valve from the outside.
German Offenlegungsschrift No. 2,159,157 discloses a a valve secured to the inside of a bag. The valve is applied either after the bag has been formed or it is secured to the packing material when it is still in a sheet form. For applying the valve to the wrapper, there is provided a hole punching device and a heater (welder) arranged concentrically with the punching device. By means of a horizontally displaceable feeder, a valve is brought underneath the punched-out location and is subsequently welded to the bag material.
While securing valves to completed bags requires additional manual labor, an insertion of the valves into the sheet material before the bag is formed may occur in a production line operation as the sheet material of indefinite length is intermittently advanced. In the former case, it is a disadvantage that expensive manual labor has to be resorted to and in the latter case, that is, when the valve is already attached when the bag (sleeve) is formed, care has to be taken that the forming mandrel of the bag-making machine does not tear off the valves as the sheet material is pulled thereover. Further, the punching of circular openings involves the additional expense of providing for a suction removal of the punched-out waste.